Electromagnetically-actuated printing mechanism

ABSTRACT

A printing mechanism comprises a rotary print drum having around the periphery thereof a series of circumferentially spaced-apart rows of print type, a drive system for electromagnetically rotating the print drum in an intermittent manner to successively position the rows of type in a print position, paper feed means for feeding a paper strip to be printed on past the print drum, and an electromagnetically actuated print hammer for striking one of the rows of print type while same is stationary in the print position to print the information contained on that row of type on the paper strip. The drive system comprises a ratchet wheel connected to the print drum, two pawls engageable with different teeth of the ratchet wheel, two electromagnets responsive to alternate pulse signals for electromagnetically reciprocating the pawls in alternate sequence to effect intermittent rotation of the print drum, and an electric control circuit for alternately applying pulse signals to the electromagnets. The operation of the paper feed means is synchronized with the rotation of the print drum to incrementally advance the paper strip one space per one revolution of the print drum and the print hammer is electromagnetically actuated one time during each revolution of the print drum to strike one of the rows of type while same is at rest in the print position.

United States Patent [191 Kawakami et al.

[ ELECTROMAGNETICALLY-ACTUATED PRINTING MECHANISM [75] Inventors: Tsuneta Kawakami, Funabashi;

Seiki Mizutani, Matsudo; Yasuyoshi Kaneda, Tokyo, all of Japan [73] Assignee: Kabushiki Kaisha Seikosha, Tokyo,

Japan 22 Filed: Aug. 16,1972

211 Appl. No.: 281,188

[30] Foreign Application Priority Data Aug. 17, 1971 Japan 46-62472 [52] US. Cl 101/93 C, 74/143, 74/577 [51] Int. Cl B4lj 7/48 [58] Field of Search 101/93 C; 310/23; 197/18, 197/53; 74/128, 143, 577 M, 557 R, 142,

[56] References Cited UNITED STATES PATENTS 1,743,478 l/l930 Pratt 74/143 3,020,774 2/1962 Kullmann 74/143 3,100,440 8/1963 Wales 101/93 C 3,139,818 7/1964 Koehn '101/93 C 3,168,182 2/1965 Bernard et a1. 197/18 3,278,725 10/1966 Gunst 235/92 3,307,676 3/1967 Hickerson 101/93 C 3,399,753 9/1968 Ravelle 101/93 C 3,493,830 2/1970 Sebastian 318/602 3,541,954 11/1970 Speicher et al. 310/23 3,626,452 12/1971 Winter et al 74/143 1 July 9,1974

Disclosure Bulletin, Vol. 3, No. 11, May 1961, page 13.

Primary ExaminerRobert E. Pulfrey Assistant Examiner-William Pieprz Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato; Bruce L. Adams [57] ABSCT A printing mechanism comprises a rotary print drum having around the periphery thereof a series of circumferentially spaced-apart rows of print type, a drive system for electromagnetically rotating the print drum in an intermittent manner to successively position the rows of type in a print position, paper feed means for feeding a paper strip to be printed on past the print drum, and an electromagnetically actuated print hammer for striking one of the rows of print type while same is stationary in the print position to print the information contained on that row of type on the paper strip. The drive system comprises a ratchet wheel connected to the print drum, two pawls engageable with different teeth of the ratchet wheel, two electromagnets responsive to alternate pulse signals for electromagnetically reciprocating the pawls in alternate sequence to effect intermittent rotation of the print drum, and an electric control circuit for alternately applying pulse signals to the electromagnets. The operation'of the paper feed means is synchronized with the rotation of the print drum to incrementally advance the paper strip one space per one revolution of the print drum and the print hammer is electromagnetically actuated one time during each revolution of the print drum to strike one of the rows of type while same is at rest in the print position.

9 Claims, 6 Drawing Figures ELECTROMAGNETICALLY ACTUATED PRINTING NECHANISM The present invention relates to a printing mechanism and more particularly to a printing mechanism having a rotary print drum and means for electromagnetically rotating the drum in an intermittent manner to effect a printing operation.

In conventional printing mechanisms, a continuously operating motor is employed as the power source for rotationally driving a rotary print drum. The print drum contains a plurality of rows of print type angularly spaced around the periphery thereof and a print hammer is positioned along the print drum to selectively strike desired ones of the rows of type to effect a printing operation. A paper strip is advanced between the print drum and the print hammers and the motor rotates the print drum either continuously or interrnit tently to successively position the various rows of type in aligned opposition to the print hammer.

The disadvantage of the prior art printing mechanisms is that the motor occupies considerable space within the printing mechanism and thus it is not possible to construct the printing mechanism as a miniature small-sized unit. The motor is an expensive component and consequently the price of the printing mechanism must reflect the cost of the motor.

In those printing mechanisms wherein the print drum is continuously rotated, an angle detecting device is necessary in order to detect the angular position of the print drum to effect actuation of the print hammer in synchronization with the rotation of the print drum. The angle detecting devices heretofore employed are complex structure requiring precise manufacturing accuracy, frequent maintenance and adjustment, and therefore require much labor and expense.

In the printing mechanisms wherein the print drum is intermittently rotated, some type of mechanical lostmotion device must be coupled to the motor in order to convert the continuous rotation of the motor output shaft into an intermittent rotation to intermittently drive the print drum. Thus a Geneva mechanism or other similarly functioning mechanism must be included within the printing mechanism and such renders the mechanism more complex and expensive. Moreover, some device must be provided for coordinating the intermittent motion of the print drum with the actuation of the print hammer. I

It is therefore a primary object of the present invention to provide a printing mechanism which is smallsized, inexpensive to manufacture, reliable in operation, high in printing accuracy, and which is suitable for use in a desk-type electronic calculator, a measuring instrument, or a terminal device of a communication machine.

It is another object of the present invention to provide a printing mechanism having an electric control circuit for controlling the actuation of the various components to effect a printing operation.

It is still further object of the present invention to provide a printing mechanism utilizing an electromagnetically driven ratchet wheel asthe power source instead of a motor therefore simplifying the structural composition of the mechanism.

The above and other objects of the present invention are carried out by a printing mechanism composed of a print drum having around the periphery thereof a set of circumferentially spaced-apart rows of print type, drive means for rotationally driving the print drum in an intermittent manner to successively position the rows of print type in a print position, paper feed means for feeding a paper strip to be printed on past the print drum, and printing means coacting with the print drum for effecting a printing operation whenever the print drum is at rest with one of the rows of print type in the print position. The drive means comprises a ratchet wheel connected to the print drum, a pawl in engagement with the ratchet wheel, an electromagnet for reciprocally driving the pawl to effect intermittent rotational movement of the ratchet wheel, and an electric control circuit for controlling the energization of the electromagnet.

The printing means comprises a print hammer pivotable into contact with one of the rows of print type on the print drum when that row of type is in the print position, and an electromagnet for'electromagnetically actuating the print hammer to cause same to strike the desired row of type to effect a printing operation. The paper feed means includes a pair of paper feed rollers having sandwiched therebetween the paper strip, a pawl-and-ratchet device connected to one of the rollers to effect intermittent rotation of the rollers in response to reciprocal movement of the pawl, and an electromagnet for reciprocally driving the pawl thereby effecting intermittent advancement of the paper strip between the print drum and the print hammer.

Having in mind the above and other objects that will be evident from an understand of the disclosure, the present invention comprises the combination and arrangement of parts illustrated in the presently preferred embodiments of the invention which are hereinafter set forth in sufficient detail to enable those persons skilled in the art to clearly understand the function, operation, construction, and advantages of them when read in conjunction with the accompanying drawings, wherein like reference characters denote like parts in the various views, and wherein:

FIG. 1 is an elevational perspective view of the mechanical components of one embodiment of the printing mechanism according to the present invention;

FIG. 2 is a block diagram of an electric control circuit for controlling the actuation of the printing mechanism shown in FIG. 1;

FIG. 3 is a series of waveforms of certain signals developed in the circuitry of FIG. 2;

FIG. 4 is an elevational perspective view of the mechanical components of another embodiment of the printing mechanism according to the present invention;

FIG. 5 is a block diagram of an electric control circuit for controlling the actuation of the printing mechanism shown in FIG. 4; and

FIG. 6 is a series of waveforms of various signals developed in the circuitry shown in FIG. 5.

One embodiment of a printing mechanism is shown in FIG. 1 and comprises print drum drive means A for intermittently rotating a print drum, printing means B coacting with the print drum for printing information on a paper strip or paper record medium P, and paper feed means C for advancing the paper record medium between the print drum and printing means. The print drum comprises a rotary print drum I mounted on a rotary shaft 2. The periphery of the print drum 1 is divided into sixteen equal circumferentially spaced-apart segments and a row of print type extends longitudinally along the length of the drum in each segment. Thus the print drum is provided with sixteen angularly spacedapart rows of type and may effect the printing of sixteen separate and distinct bits information depending upon the angular position of the print drum.

The print drum drive means A for intermittently driving the print drum in angular increments comprises a ratchet wheel 3 connected to one end of the shaft 2 and having around the periphery thereof 16 similarly dimensioned ratchet teeth. A drive lever 4 is mounted for pivotal movement about a pin 5 affixed to a frame portion of the printing mechanism. A pawl 6 is pivotally mounted on the distal end of the driving lever 4 by means of a pin 7. The pawl 6 is biased into constant contact with a tooth. of the ratchet wheel by a biasing spring 8 and another biasing spring 9 continuously urges the drive lever 4 towards an initial limit position wherein the tip of the pawl 6 rests upon a flank portion of one of the ratchet teeth.

A stop member 11 defines the initial limit position of the drive lever 4 wherein the drive lever abuts against the stop member 11 and is maintained thereagainst by the biasing spring 9. Another stop member defines the terminal limit position of the drive lever 4 wherein a surface portion of the pawl 6 abuts against the stop member 10 to limit the extent of clockwise movement of the drive lever 4 effected by the actuating means described below. Thus it may be seen that the drive lever 4 is mounted for pivotal movement between two limit positions defined by the stop members 10 and 11.

Actuating means l2, 13 effects reciprocal pivotal movement of the drive lever 4 between the two limit positions. The actuating means comprises an armature 12 affixed to the drive lever 4 at a location adjacent the pin 5 and an electromagnet 13 is affixed to a frame portion of the printing mechanism in opposed relationship from the armature 12. When the electromagnet 13 is energized, a magnetic field is created therearound which coacts with the armature 12 to attract the anna ture 12 towards the electromagnet thereby pivoting the drive lever 4 in a clockwise direction. The gap spacing between the armature l2 and the electromagnet 13 is suitably chosen in relation to the pitch of each two adjoining ratchet teeth such that movement of the drive lever from the initial limit position wherein the drive lever 4 abuts against the stop member 11 to the terminal limit position (shown in FIG. 1) wherein the pawl 6 abuts against the stop member 10 causes the pawl 6 to angularly advance the ratchet wheel 3 a distance equal to one ratchet tooth thereby advancing the print drum an angular increment equal to one/sixteenth of a revolution. When the electromagnet 13 is deenergized, the magnetic field collapses and the force of attraction between the armature 12 and the electromagnet terminates after which the biasing spring 9 urges the drive lever 4 in a counterclockwise direction back to the initial limit position. A detent lever 14 engages with the ratchet wheel 3 to maintain same in its advanced position.

The printing means B comprises a hammer lever 15 pivotally mounted on a shaft 16. The hammer lever 15 has two lever arms and a hammer head 17 is connected to the distal end of one lever arm and an armature 18 is connected to the distal end of the other lever arm. A biasing spring 19 biases the hammer lever 15 in a clockwise direction into abutment with a stop member 20.

An electromagnet 21 is affixed to a frame portion of the printing mechanism in opposed, spaced relationship from the armature l8 and is intermittently energized by electric signals to intermittently attract the armature thereto to effect reciprocal pivotal movement of the hammer lever 15.

The hammer head 17 is dimensioned and positioned relative to the print drum 1 to strike the surface of the print drum in response to pivotal movement of the hammer lever 15. During operation of the printing means, the electric signal applied to the electromagnet 21 is synchronized with the pulse signals applied to the electromagnet 13 so that the hammer head 17 strikes a preselected row of print type contained on the print drum 1 to effect the desired printing operation. The hammer lever 15 is actuated one time per each sixteen incremental angular movements of the print drum 1 and therefore any one of the sixteen rows of type may be printed on the paper strip P duringone printing cycle.

An ink roller 22 is rotatably mounted by means of a shaft 23 onto a frame portion of the printing mechanism. The periphery of the ink roller 22 is maintained in a frictional contact with the peripheral surface of the print drum 1 and the ink roller applys ink to the rows of print type on the print drum during their combined rotation. Means (not shown) is provided for supplying ink to the ink roller 22 in a conventional manner.

The paper feed means C comprises a feed roller 24 rotatably mounted on a shaft 25 and a supplementary feed roller 26 rotatably mounted on a shaft 27. The paper record medium P is sandwiched between the feed roller 24 and the supplementary feed roller 26 and the latter roller is mounted for slight movement towards and away from the feed roller 24 to selectively adjust the degree of pressure contact between the two rollers and the paper strip P.

A ratchet wheel 28 is connected to the feed roller 24 and is also mounted on the shaft 25. A lever 30 is pivotally mounted at one end on a pin 29 and a pin 31 projects outwardly from the other end of the lever 30. The pin 31 coacts with the ratchet wheel 28 to angularly advance the ratchet wheel 28 in a counterclockwise direction in response to pivotal movement of the lever 30 in a clockwise direction. A biasing spring 32 biases the lever 30 in a counterclockwise direction as shown in FIG. 1.

A link 33 is pivotally attached at one end to the lever 30 intermediate the pins 29 and 31. The other end of the link 33 is pivotally attached to an armature 34 of an electromagnet 35. When the electromagnet 35 is energized, a magnetic field is created which coacts with the armature 34 to pull the armature inwardly into the electromagnet thereby pivoting the lever 30 in a clockwise direction through an angular distance sufficient to advance the ratchet wheel 28 one pitch. When the electromagnet 35 is deenergized, the biasing spring 32 returns the lever 30 to its start position. During angular advancement of the feed roller 24, the feed roller coacts with the supplementary feed roller 26 to advance the paper record medium P towards the print drum 1.

FIG. 2 discloses a block diagram of the control circuitry for effecting intermittent rotation of the print drum 1. A commercial power source 37 supplies electric power for actuating the printing mechanism and the power source provides a standard signal having a frequency of 50 or 60 cycles per second. A Schmitt circuit 38 receives the signal from the power source and converts same into a succession of output pulse signals having a waveform such as shown in FIG. 3a.

Gate means D receives the pulse signals from the Schmitt circuit 38 and applies them to the electromagnet 13 in a controlled manner to control the energization periods of the electromagnet. The gate means D comprises an AND gate 39 having two inputs and one output. One input of the AND gate 39 receives the succession of pulse signals from the Schmitt circuit 38 and delivers them to the output only when a gate signal is applied to the other input. A flip-flop circuit 41 has a trigger input T for receiving a print command signal 40, a reset input Rd, and an output Q connected to the other input of the AND gate 39. The flip-flop circuit 41 has a set state and a reset state and when in the set state, an output signal is produced at the output Q and when in the reset state, no output signal is produced at the output 0.

In accordance with the present invention, the output signal from the output Q is used as a gate signal to place the AND gate 39 in a gating state to enable same to gate the pulse signals to the electromagnet 13. In the absence of the gate signal, the AND gate 39 is in a blocking state blocking the application of pulse signals to the electromagnet. The waveform of the gate signal is shown in FIG. 3b and it may be seen that the gate signal has a duration equal to 16 pulse signals and thus during the application of each gate signal, the AND gate 39 enables 16 pulse signals to be applied to the electromagnet 13. The waveform of the AND gate output is shown in FIG. 30. i

A counter 42 is connected to receive the pulse signals from the output of the AND gate 39 and the counter counts 16 pulse signals and then delivers a reset signal to the reset input Rd of the flip-flop circuit 41 to reset the circuit in its reset state in'readiness to receive another print command signal. Thus, in one printing cycle, a print command signal 40 is applied to the trigger input T of the flip-flop circuit 41 to trigger same to its set state wherein a gate signal is delivered from the output 0 to the AND gate 39 to place the latter in a gating state to gate the pulse signals to the electromagnet 13. The pulse signals fed to the electromagnet 13 are also applied to the counter 42 and the counter then counts 16 pulse signals and applies a reset signal to the flipflop circuit 41 to reset same into its reset state wherein no gate signal is delivered from the output 0.

The print command signal 40 is derived from a control device of an electronic calculator (not shown) or from another suitable source. It is understood that a rectifier may be used in place of the Schmitt circuit 38 to develope a succession of pulse signals.

During the operation of the embodiment shown in FIG. 1, the ratchet wheel 3 is rotationally driven in an intermittent manner to angularly displace the print drum 1 through 16 angular increments per revolution. During the time that any one of the 16 rows of type is at rest in the print position wherein same is aligned opposite to the hammer head 17, a signal is applied to the electromagnet 21 to pivot the hammer lever to cause the hammer head 17 to strike the desired row of type to effect a printing operation. When the print drum 1 has completed one revolution, an electric signal is applied to the electromagnet 35 to energize the electromagnet to effect pivotal movement of the lever 30 to displace the ratchet wheel 38 one pitch thereby advancing the paper record medium P between the print drum 1 and the print hammer 17 one space.

Another embodiment of print drum drive means A is shown in FIG. 4 and such comprises a print drum la mounted on a rotatable shaft 2a. and the periphery of the drum is provided with sixteen angularly spacedapart rows of type. Also mounted on the shaft 2a is a ratchet wheel 43 having eight ratchet teeth all having the same shape.

An actuating lever 44 is pivotally mounted on a shaft 45 and a drive pin 46 projects outwardly from the upper end of the actuating lever 44. The lower end of the actuating lever 44 comprises an armature and a pair of electromagnets 47 and 48 are positioned in opposed facing relationship on either side of the actuating lever 44. By such an arrangement, alternate energization of the electromagnets 47 and 48 effect reciprocal pivotal movement of the actuating lever 44.

A plate member 49 is pivotally mounted on a pin 50 beneath the ratchet wheel 43. The plate member has a slot 51 in which is received the drive pin 46 and by such a pin-and-slot connection, pivotal movement of the actuating lever 44 in the counterclockwise direction caused by energization of the electromagnet 47 effects clockwise pivotal movement of the plate member 49, whereas pivotal movement of the actuating lever 44 in the clockwise direction caused by energization of the electromagnet 48 effects pivotal movement of the plate member 49 in a counterclockwise direction. The plate member has a recess 53 in one side thereof and a stop member 52 is mounted within this recess. The stop member alternately abuts with opposite sides of the recess to limit the extent of pivotal movement of the plate member 49.

A pair of pawls 54 and 55 are tumably mounted at the respective upper corners of the plate member 49. A biasing spring 56 urges the pawl 54 into continuous contact with a tooth of the ratchet wheel 43 and a biasing spring 57 urges the pawl 55 into continuous contact with a different tooth of the ratchet wheel. Another biasing spring 58 functions as a clik spring and maintains the plate member 49 in a stationary state during the time that neither electromagnet is energized.

A stop pin 59 is positioned as shown in FIG. 4 and coacts with the pawl 55 to limit the driving movement of the pawl when the plate member 49 is pivoted in a clockwise direction. A similarly functioning stop pin 60 is'provided to limit the extent of, driving movement of the pawl 54 in response to pivotal movement of the plate member 49 in a counterclockwise direction. A detent lever 62 is pivotally mounted on a pin 61 and has at its distal end a pair of detents 63 and 64. The detents 63 and 64 alternately and releasably engage with each tooth of the ratchet wheel 43 to maintain the print drum la in each advanced position.

The operation of the FIG. 4 embodiment will now be described. In the state shown, the electromagnet 47 is energized and attracts the actuating lever 44 causing same to pivot in a counterclockwise direction thereby pivotally actuating the plate member 49 in a clockwise direction and causing the pawl 55 to engage with and drive and ratchet wheel 43 one/half pitch. In this state, the stop pin 59 limits the extent of movement of the pawl 55 and the detent 64 engages with a tooth of the ratchet wheel to maintain the print drum lain the position shown.

When the electromagnet 48 is energized, the actuating lever 44 is pivoted in a clockwise direction thereby pivotally actuating the plate member 49 in a counterclockwise direction causing the pawl 54 to slide into engagement with a tooth of the ratchet wheel 43 and advance the ratchet wheel by one/half pitch. As the pawl 54 moves leftward in driving the ratchet wheel 43, the pawl abuts against the stop pin 60 which effectively limits the extent of driving movement of the pawl. During this time, the detent 63 slides into engagement with the next tooth on the ratchet wheel to maintain the print drum 1a in this new position. Each time one of the electromagnets 47 and 48 is energized, the print drum 1a is advanced through one/half pitch or one/sixteenth of a revolution and each time the pair of electromagnets are once energized, the print drum la is advanced one pitch of the ratchet wheel 43 which corresponds to two/sixteenths of a revolution of the print drum. Thus, alternate energization of the electromagnets 47 and 48 effects intermittent rotational movement of the print drum 1a.

The control circuitry for energizing the electromagnets 47 and 48 is shown in FIG. 5. Like the embodiment shown in FIG. 1, a commercial power source 65 supplys power at a standard 50 or 60 cycles per second and a Schmitt circuit 66 receives the standard signal and converts same into a pulse train having a waveform such as shown in FIG. 6a. Gate means E responds to a print command signal 68 to apply a succession of pulse signals to the electromagnets through a circuit F.

The gate means E is identical to the gate means D shown in FIG. 2 and comprises an AND gate 67 having two inputs and one output and a flip-flop circuit 69 having an output 0, a trigger input T, and a reset input Rd. The output of the flip-flop circuit 69 is connected to one input and the AND gate 67 the other input of the AND gate is connected to the Schmitt circuit 66 to receive therefrom the pulse train. The flipflop circuit 69 has a set state and a reset state and when in the set state, an output signal having a waveform shown in FIG. 6b is applied from the output 0 and this output signal functions as a gate signal to place the AND gate 67 in its gating mode. When the fiip-flop cit-- cuit 69 is in its reset state, no output signal is delivered from the output Q and thus no gate signal is applied to the AND gate 67. Whenever the flip-flop circuit is in its reset state, a print command signal 68 applied to the trigger input T flips the circuit to the set state to apply a gate signal to the AND gate 67.

The circuit F for supplying pawl-actuating pulse signals to the electromagnets 47 and 48 comprises a flipflop circuit 70 having a trigger input T connected to the output of the AND gate 67, an output Q connected to an AND gate 71, and another output 0 connected to an AND gate 72. The AND gates 71 and 72 each have an input connected to the output of the AND gate 67 to receive the succession of pulse signals delivered from the AND gate 67 and the output of the AND gate 71 is connected to the electromagnet 47 whereas the output of the AND gate 72 is connected to the electromagnet 48.

The flip-flop circuit 70 has a set state wherein the output 0 applies a gate signal to the AND gate 71 and the waveform of this gate signal is shown in FIG. 60,, and a reset state wherein the output 0 applies a gate signal to the AND gate 72 and the waveform of this gate signal is shown in FIG. 60 A counter 73 functions in a manner similar to the counter 42 shown in FIG. 2 and is connected to receive the pulse signals from the AND gate 67 and counts sixteen pulses and then applies a reset signal to the flip-flop circuit 69.

The control circuitry operates in the following manner to alternately energize the electromagnets 47 and 48. The pulse train applied to the AND gate 67 from the Schmitt circuit 66 is blocked by the gate 67 until a gate signal is applied from the flip-flop circuit 69 to place the AND gate 67 in its gating state. The flip-flop circuit 69 is normally in its reset state and is triggered to the set state by a print command signal 68 applied to the trigger input T whereupon a gate signal is delivered from the output Q and applied to the AND gate 67 to place same in its gating state. This gating signal is shown in FIG. 6b.

Thus the succession of pulse signals applied to the AND gate 67 is applied simultaneously to one input of each of the AND gates 71 and 72 as well as to the counter 73 and the trigger input T of the flip-flop circuit 70. Each successive pulse triggers the flip-flop circuit 70 back and forth between the set state and the reset state causing alternate pulses to be delivered from the outputs output Q and Q to alternately place the AND gates 71 and 72 in their gating state. As seen in FIGS. 60 and 6c the gate signals applied to the AND gates 71 and 72 are out of phase with each other and correspond to alternate ones of the pulse signals applied to the AND gate 67 by the Schmitt circuit 66.

The AND gates 71 and 72 are thereby alternately placed in their gating and blocking states and alternate ones of the pulse signals delivered from the AND gate 67 are alternately gated by the AND gates 71 and 72 to alternately energize the electromagnets 47 and 48 to effect intermittent rotation of the print drum la. The counter 73 counts 16 pulses and then applies a reset signal to the flip-flop circuit 69 to place same in its reset state thereby terminating the application of the gate signal to the AND gate 67 and placing same in its blocking state until the next print command signal 68 is delivered.

It is understood that the Schmitt circuit 66 may be replaced by a full-wave or a half-wave rectifier. Moreover, those skilled in the art will recognize that a single electromagnet having a hook-shaped core may be used instead of the pair of electromagnets disclosed in FIG.

4 and in this instance, two signals of different polarity would be alternately supplied to the exciting coil wound around the core. Also, the present invention is useable with other kinds of print type mechanisms aside from a rotary print drum and a type belt or other device may be used without departing from the present invention.

. The invention has been described in conjunction with two particular embodiments and it is understood that obvious modifications and changes may be made without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. In a printing mechanism for printing information on a record medium: a movable type-carrying member carrying thereon n sets of print type successively spaced apart from each other in the direction of movement of said type-carrying member; electromagnetic drive means responsive to n electric pulse signals for electromagnetically driving said type-carrying member in an intermittent manner in one direction through n equal increments each effected by one pulse signal to effect successive intermittent movement of each set of print type into a common print position thereby defining one printing cycle, said electromagnetic drive means comprising a rotatable ratchet wheel having a set of n/2 ratchet teeth, means connecting said ratchet wheel to said type-carrying member to effect intermittent movement of said type-carrying member in response to intermittent stepwise rotation of said ratchet wheel, a pair of pawls each in engagement with different ratchet teeth of said ratchet wheel and alternately coacting with said ratchet wheel to effect intermittent stepwise movement of said ratchet wheel in response to reciprocatory movement of alternate ones of said pawls, means biasing said pawls into continuous contact with different ratchet teeth of said ratchet wheel, a pivotal plate member having said pawls tumably mounted thereon and operative to alternately reciprocate said pawls in response to reciprocatory pivotal movement of said plate member, means including a pair of electromagnets operative when alternately energized with pulse signal to effect reciprocatory pivotal movement of said plate member thereby intermittently driving said type-carrying member and advancing same through equal increments and means engagable with said ratchet teeth for releasably holding said ratchet wheel and thereby said type carrying member in each successive advanced position; control circuit means for selectively developing pulse trains composed of n electric pulse signals and applying alternate ones of the pulse signals to respective ones of said pair of electromagnets to effect alternate energization thereof to control the movement of said type-carrying member; and printing means coacting with said type-carrying member for striking one of said sets of print type when same is stationary in said print position to print the information contained on that set of print type on a record medium.

2. A printing mechanism according to claim 1; wherein said control circuit means comprises gate means receptive of a continuous train of pulse signals and having a gating state wherein same gates pulse signals to said electromagnetic drive means in response to receipt of a print command signal and a blocking state wherein same blocks the application of pulse signals to said electromagnetic drive means in response to receipt of a blocking signal, and counting means for counting the number of pulse signals gated by said gate means and developing a blocking signal after counting n pulse signals and applying said blocking signal to said gate means to place same in its blocking state until receipt of another print command signal.

3. A printing mechanism according to claim 2; wherein said gate means comprises an AND gate receptive of said continuous train of pulse signals and operative to gate same to said electromagnetic drive means in response to and during the presence of a gate signal I wherein same delivers no output gate signal to said AND gate in response to receipt of the output signal from said counter means.

4. A printing mechanism according to claim 2; wherein said control circuit means comprises an AND gate connected to each electromagnet, each AND gate being connected to receive the pulse signals from said gate means and operative to apply same to its respective electromagnet in response to receipt of a gate signal, and a flip-flop circuit having a first stable state wherein same delivers an output gate signal to one AND gate and a second stable state wherein same delivers an output gate signal to the other AND gate and having a trigger input receptive of said pulse signals from said gate means to alternately trigger said flip-flop circuit into its first and second stable states in response to alternate pulse signals.

5. A printing mechanism according to claim 2; wherein said type-carrying member comprises a rotary print drum having around the periphery thereof n circumferentially spaced-apart and longitudinally extending rows of print type.

6. A printing mechanism according to claim 2; wherein said printing means comprises a pivotal lever having a pair of lever arms, a print hammer connected to one lever arm and movable into contact with one of said sets of print type when same is in said print position in response to pivotal movement of said lever, an armature connected to the other lever arm, and an electromagnet selectively energizeable to create therearound a magnetic field coacting with said armature to attract said armature towards said electromagnet to effect pivotal movement of said lever.

7. A printing mechanism according to claim 2; including feeding means for intermittently feeding a record medium between said printing means and said type-carrying member one space per printing cycle.

8. A printing mechanism according to claim 7; wherein said feeding means comprises a pair of rotatable feed rollers having sandwiched therebetween and in frictional driving contact therewith the record medium, and electromagnetic means for electromagnetically rotating one of said feed rollers in an intermittent manner through a succession of angular increments to intermittently feed the record. medium one space per angular increment of movement of said one feed roller.

limit the extent of driving movement of said pawls. 

1. In a printing mechanism for printing information on a record medium: a movable type-carrying member carrying thereon n sets of print type successively spaced apart from each other in the direction of movement of said type-carrying member; electromagnetic drive means responsive to n electric pulse signals for electromagnetically driving said type-carrying member in an intermittent manner in one direction through n equal increments each effected by one pulse signal to effect successive intermittent movement of each set of print type into a common print position thereby defining one printing cycle, said electromagnetic drive means comprising a rotatable ratchet wheel having a set of n/2 ratchet teeth, means connecting said ratchet wheel to said type-carrying member to effect intermittent movement of said type-carrying member in response to intermittent stepwise rotation of said ratchet wheel, a pair of pawls each in engagement with different ratchet teeth of said ratchet wheel and alternately coacting with said ratchet wheel to effect intermittent stepwise movement of said ratchet wheel in response to reciprocatory movement of alternate ones of said pawls, means biasing said pawls into continuous contact with different ratchet teeth of said ratchet wheel, a pivotal plate member having said pawls turnably mounted thereon and operative to alternately reciprocate said pawls in response to reciprocatory pivotal movement of said plate member, means including a pair of electromagnets operative when alternately energized with pulse signal to effect reciprocatory pivotal movement of said plate member thereby intermittently driving said type-carrying member and advancing same through equal increments and means engagable with said ratchet teeth for releasably holding said ratchet wheel and thereby said type carrying member in each successive advanced position; control circuit means for selectively developing pulse trains composed of n electric pulse signals and applying alternate ones of the pulse signals to respective ones of said pair of electromagnets to effect alternate energization thereof to control the movement of said type-carrying member; and printing means coacting with said type-carrying member for striking one of said sets of print type when same is stationary in said print position to print the information contained on that set of print type on a record medium.
 2. A printing mechanism according to claim 1; wherein said control circuit means comprises gate means receptive of a continuous train of pulse signals and having a gating state wherein same gates pulse signals to said electromagnetic drive means in response to receipt of a print command signal and a blocking state wherein same blocks the application of pulse signals to said electromagnetic drive means in response to receipt of a blocking signal, and counting means for counting the number of pulse signals gated by said gate means and developing a blocking signal after counting n pulse signals and applying said blocking signal to said gate means to place same in its blocking state until receipt of another print command signal.
 3. A printing mechanism according to claim 2; wherein said gate means comprises an AND gate receptive of said continuous train of pulse signals and operative to gate same to said electromagnetic drive means in response to and during the presence of a gate signal and operative to block the application of pulse signals during the absence of a gate signal, and a flip-flop circuit operative in one stable state wherein same delivers an output gate signal to said AND gate in response to said print command signal and another stable state wherein same delivers no output gate signal to said AND gate in response to receipt of the output signal from said counter means.
 4. A printing mechanism according to claim 2; wherein said control circuit means comprises an AND gate connected to each electromagnet, each AND gate being connected to receive the pulse signals from said gate means and operative to apply same to its respective electromagnet in response to receipt of a gate signal, and a flip-flop circuit having a first stable state wherein same delivers an output gate signal to one AND gate and a second stable state wherein same delivers an output gate signal to the other AND gate and having a trigger input receptive of said pulse signals from said gate means to alternately trigger said flip-flop circuit into its first and second stable states in response to alternate pulse signals.
 5. A printing mechanism according to claim 2; wherein said type-carrying member comprises a rotary print drum having around the periphery thereof n circumferentially spaced-apart and longitudinally extending rows of print type.
 6. A printing mechanism according to claim 2; wherein said printing means comprises a pivotal lever having a pair of lever arms, a print hammer connected to one lever arm and movable into contact with one of said sets of print type when same is in said print position in response to pivotal movement of said lever, an armature connected to the other lever arm, and an electromagnet selectively energizeable to create therearound a magnetic field coacting with said armature to attract said armature towards said electromagnet to effect pivotal movement of said lever.
 7. A printing mechanism according to claim 2; including feeding means for intermittently feeding a record medium between said printing means and said type-carrying member one space per printing cycle.
 8. A printing mechanism according to claim 7; wherein said feeding means comprises a pair of rotatable feed rollers having sandwiched therebetween and in frictional driving contact therewith the record medium, and electromagnetic means for electromagnetically rotating one of said feed rollers in an intermittent manner through a succession of angular increments to intermittently feed the record medium one space per angular increment of movement of said one feed roller.
 9. A printing mechanism according to claim 1; wherein said electromagnetic drive means includes stop pins positioned relative to said pair of pawls to limit the extent of driving movement of said pawls. 